TDDB68/TDDE47 Concurrent Programming and Operating

Systems

Lecture 1: Introduction, interrupts and system calls

Mikael Asplund

Copyright Notice: The lecture notes are partly based on Silberschatz’s, Galvin’s and Gagne’s book (“Operating System Concepts”, 7th ed., Wiley, 2005). No part of

the lecture notes may be reproduced in any form, due to the copyrights reserved by Wiley. These lecture notes should only be used for internal teaching purposes at the Linköping University.

Hardware

Hardware

Prog1

Hardware

Prog1 Prog2 Prog3 Prog4

Hardware

Operating System

Prog1 Prog2 Prog3 Prog4

1. Do this2. Do that3. Wait for X4. Send Y5. Do something6. Wait a while7. Do something else

1. Send Z2. Wait for X3. Do nothing4. Send something else5. Do this

1. Wait for query2. Connect to database3. Send db-query4. Wait for results5. Create web page6. Reply to request

Concurrency

In this course:

Focus on basic principles

Courses

● TDDB68: 6hp course for D + U + I + M.Sc. + Erasmus– C/C++ with pointers a prerequisite

● TDDE47: 8hp course for IT– More time and some PBL sessions for learning about

memory allocation and pointers

● TDDE47 and TDDB68 have the same exam and labs.

Course web

● TDDB68:– https://www.ida.liu.se/~TDDB68/

● TDDE47– https://www.ida.liu.se/~TDDE47/

● Same content – report if anything is strange

People

● Examiner: Mikael Asplund● Course assistant: Felipe Boeira● Lab assistants:

– TDDB68 Group A: Felipe Boeira– TDDB68 Group B: Rodrigo Saar Moraes– TDDB68 Group C: Jesper Jonsson– TDDB68 Group D: Anna Montelius– TDDB68 Group E: Nils Broman– TDDB68 Group F: Olivia Shamon– TDDE47 group: Erik Norrestam Held

Examination

● Labs 3hp for TDDB68, 5hp for TDDE47

● Written exam 3hp

● Bonus assignment 0hp– 3p bonus points on the exam– Pass all labs no later than 2021-03-11– Need to be first-time registered in VT1 2021

Labs

● Pintos– Stanford educational OS

● Challenging!

● Register in webreg today– Only new students!

Deadlines

● 2021-01-22 Sign up in webreg (new students)

● 2021-03-11 Lab deadline to get the bonus points on the exam

● 2021-03-29 Last chance to pass the labs in VT1

Lab feedback

● Promise: – No later than 2w from the soft deadline – Lab6 at least one chance to correct if you hand in on the 11th

● Soft deadlines:– Lab0: January 29– Lab1: February 5– Lab2: February 15– Lab3: February 21– Lab4: February 27– Lab5: March 4– Lab6: March 10

Time management

● Lectures 8*2h + 1*4h

● Lessons 3*2h (to prepare for labs)

● Labs 36h (42 for TDDE47)

● Self-study TDDB68: ~100h, TDDE47: ~145h

Time management

● Lectures 8*2h + 1*4h

● Lessons 3*2h (to prepare for labs)

● Labs 36h (42 for TDDE47)

● Self-study TDDB68: ~100h, TDDE47: ~145h

If you’re not spending 10+ hours/week of free timedoing labs

and studying for this course,you will be in trouble.

Do not cheat!

● Labs are hard and you might find solutions online

● It is not allowed to copy anyone else’s solution

● We are obliged to report suspected plagiarism to the disciplinary board

Course book

Exam

● Previous exams available (for 2020 only part C)

● Solutions not available

● Most likely: remote exam– Part A: multiple choice– Part B: basic questions– Part C: more advanced questions

For grade 3

→ For grade 4&5

Lectures vs. Labs

● Intentionally different scope

● Lectures provide an overview of a vast area

● Labs provide hands-on experience with a particular educational OS.

Results from Evaliuate

TDDB68 TDDE47

Two comments:

”Put more emphasis on telling the students to read the book. I didn't understand much during the lectures because I didn't read the book until the exam period. Had I read the pages before each lecture, the lectures would have been more productive.”

”... And the book was actually really good - I wish I had started reading it before the exam period.”

Planned changes

● Distance mode – Not by choice, but still quite time consuming

● Will add some exercises– Has been requested– Hopefully helps to study for exam

What does an operating system do?

Instruction Fetch

Instruction Decode

Instruction Execute

Update Program Counter

Program execution (von Neumann cycle) by a processor

1. Do this2. Do that3. Wait for X4. Send Y5. Do something6. Wait a while7. Do something else

1. Send Z2. Wait for X3. Do nothing4. Send something else5. Do this

1. Wait for query2. Connect to database3. Send db-query4. Wait for results5. Create web page6. Reply to request

How to do concurrency?

Interrupts

Instruction Fetch

Instruction Decode

Instruction Execute

Update Program Counter

Check for Interrupt

No

Yes

Execute interrupt service routine (ISR)

Restore processor state

Save processor state

Software Interrupts● A trap is a software-generated interrupt

caused either by an error or a user request.

– Examples: Division by zero; Request for OS service

An operating system is interrupt driven.

Why not just have a function API?

Dual Mode

Dual modeUser process Kernel CPU mode

User mode Kernel mode

Normal execution

System call(setting up)

System call(execution)

Trap!

Return

Normal execution

Types of System Calls● Process control

load, execute, end, abort, create, terminate, wait ...memory allocation and deallocation

● File managementopen, close, create, delete, read, write, get/set attributes...

● Device managementrequest / release device, read, write, ...

● Information maintenanceget / set time, date, system data, process / file attributes

● Communicationscreate / delete connection, send, receive, ...

Syscalls In Linux

(man syscalls)

Tracing system calls

Linux – ltraceMac OSX - dtrace

System Call API – OS Relationship

User mode

Kernel mode

System call interface

User processopen ( )

open ( )implementation of open ( ) system call…return

i

Hardware specific

Standard across different platforms

Example of a System Call API● ReadFile() function in Win32 API (function for reading from a file)

● Parameters passed to ReadFile():– file — the file to be read– buffer — a buffer where the data will be read into and written from– bytesToRead — the number of bytes to be read into the buffer– bytesRead — the number of bytes read during the last read– ovl — indicates if overlapped I/O is being used

System Call Parameter Passing● Three general methods used to pass parameters to

syscalls:– Parameters in registers– Parameters in a block in memory, and address to

block in a register ● This approach taken by Linux

– Parameters pushed onto the stack

● What are the advantages/disadvantages?

System Call Parameter Passing via Block

parameters for call

X:

System Programs● User's view of an Operating System

● Provide a convenient environment

– File management

– Program development

– Graphical user interface

– ...

Summary● Operating System = OS Kernel + System Programs

– Mediates all accesses to system resources– Interrupt-driven

● Error handling● Controlled access to system resources, e.g.

– I/O devices, DMA

– CPU time sharing

● …

● Dual-Mode (user mode, kernel mode)– System Call API for portability

Reading guidelines

● 9th edition– Chapter 1: Sections 1.1-1.7– Chapter 2: 2.3-2.5

● 10th edition– Chapter1: 1.1-1.5– Chapter2: 2.3-2.4

What's next?

● Today– Sign up in Webreg!– Get the book

● Tomorrow– 13-17 Introductory C lecture– Try some C programming

● Thursday– 8-10 lesson to introduce the labs

● Friday– First lab (lab0)